Pub Date : 2005-06-19DOI: 10.1109/ICT.2005.1520002
Xiaoya Li, Lidong Chen, Junfeng Fan, S. Bai
CoSb/sub 3/ based materials are promising for power generation in the intermediate temperature range. In the present work, we have developed a novel technology for the fabrication of CoSb/sub 3/ thermoelectric (TE) couple by spark plasma sintering (SPS). Molybdenum (Mo) was selected as the electrode material and a titanium (Ti) layer was inserted between Mo and CoSb/sub 3/ to realize the joining of Mo to CoSb/sub 3/ at a lower temperature. Shear tests showed that the joint possesses a shear strength ranging from 55 MPa to 70 MPa. The potential voltage measurement showed that the joint exhibits good electrical properties. All the results indicate that the Mo/Ti/CoSb/sub 3/ joining technology is suitable for fabricating TE couples using the CoSb/sub 3/ based materials.
{"title":"Mo/Ti/CoSb/sub 3/ joining technology for CoSb/sub 3/ based materials","authors":"Xiaoya Li, Lidong Chen, Junfeng Fan, S. Bai","doi":"10.1109/ICT.2005.1520002","DOIUrl":"https://doi.org/10.1109/ICT.2005.1520002","url":null,"abstract":"CoSb/sub 3/ based materials are promising for power generation in the intermediate temperature range. In the present work, we have developed a novel technology for the fabrication of CoSb/sub 3/ thermoelectric (TE) couple by spark plasma sintering (SPS). Molybdenum (Mo) was selected as the electrode material and a titanium (Ti) layer was inserted between Mo and CoSb/sub 3/ to realize the joining of Mo to CoSb/sub 3/ at a lower temperature. Shear tests showed that the joint possesses a shear strength ranging from 55 MPa to 70 MPa. The potential voltage measurement showed that the joint exhibits good electrical properties. All the results indicate that the Mo/Ti/CoSb/sub 3/ joining technology is suitable for fabricating TE couples using the CoSb/sub 3/ based materials.","PeriodicalId":422400,"journal":{"name":"ICT 2005. 24th International Conference on Thermoelectrics, 2005.","volume":"74 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2005-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124924131","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2005-06-19DOI: 10.1109/ICT.2005.1519941
E. Lee, J. Ryu, S. Bhattacharya, T. Tritt
Advanced bulk thermoelectric materials have been developed by fabricating composites of uniformly distributed thermoelectric nanoparticles within a high surface area semiconductor matrix. In this composite structure, constituents of the thermoelectric materials' figure of merit can be decoupled and controlled independently, and consequently, one can achieve a high thermoelectric figure of merit. The produced composites exhibited extremely low thermal conductivity and relatively high electrical conductivity. However, the Seebeck coefficient was relatively low, probably due to poor quality of the thermoelectric particles. In an in-plane test geometry (van der Pauw configuration), the electrical resistivity of the composite sample decreased continuously as temperature increased, a typical semiconductor behavior. In the perpendicular-to-the-plane (cross-plane) test geometry, electrical resistance of the sample increased continuously with increasing temperature, probably a semi-metallic behavior. This anisotropy in the electrical resistance was reproducible. We also observed relatively strong high frequency AC-signals in the in-plane test geometry samples.
通过在高表面积的半导体基体中制备均匀分布的热电纳米颗粒复合材料，已经开发出先进的块状热电材料。在这种复合结构中，热电材料的各组分的性能因数可以独立地解耦和控制，从而可以实现高热电性能因数。所制备的复合材料具有极低的导热性和相对较高的导电性。然而，塞贝克系数相对较低，可能是由于热电粒子的质量较差。在平面内测试几何(van der Pauw结构)中，复合材料样品的电阻率随着温度的升高而持续下降，这是典型的半导体行为。在垂直于平面(交叉平面)的测试几何形状中，样品的电阻随着温度的升高而不断增加，可能是一种半金属行为。电阻的这种各向异性是可重复的。我们还在平面内测试几何样品中观察到相对较强的高频交流信号。
{"title":"Nanostructured bulk thermoelectric materials and their properties","authors":"E. Lee, J. Ryu, S. Bhattacharya, T. Tritt","doi":"10.1109/ICT.2005.1519941","DOIUrl":"https://doi.org/10.1109/ICT.2005.1519941","url":null,"abstract":"Advanced bulk thermoelectric materials have been developed by fabricating composites of uniformly distributed thermoelectric nanoparticles within a high surface area semiconductor matrix. In this composite structure, constituents of the thermoelectric materials' figure of merit can be decoupled and controlled independently, and consequently, one can achieve a high thermoelectric figure of merit. The produced composites exhibited extremely low thermal conductivity and relatively high electrical conductivity. However, the Seebeck coefficient was relatively low, probably due to poor quality of the thermoelectric particles. In an in-plane test geometry (van der Pauw configuration), the electrical resistivity of the composite sample decreased continuously as temperature increased, a typical semiconductor behavior. In the perpendicular-to-the-plane (cross-plane) test geometry, electrical resistance of the sample increased continuously with increasing temperature, probably a semi-metallic behavior. This anisotropy in the electrical resistance was reproducible. We also observed relatively strong high frequency AC-signals in the in-plane test geometry samples.","PeriodicalId":422400,"journal":{"name":"ICT 2005. 24th International Conference on Thermoelectrics, 2005.","volume":"3 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2005-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116691556","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2005-06-19DOI: 10.1109/ICT.2005.1519895
H. Wang, W. Porter, J. Sharp
Thermal conductivity is an important material property of the bulk thermoelectrics. To improve ZT a reduced thermal conductivity is always desired. However, there is no standard material for thermoelectrics and the test results, even on the same material, often show significant scatter. The scatter in thermal conductivity made reported ZT values uncertain and sometime unrepeatable. One of the reasons for the uncertainty is due to the microstructure differences resulting from sintering, heat treatment and other processing parameters. We selected commonly used bulk thermoelectric materials and conducted thermal conductivity measurements using the laser flash diffusivity and differential scanning calorimeter (DSC) systems. Thermal conductivity was measured as a function of temperature from room temperature to 500 K and back to room temperature. The effect of thermal cycling on the bulk thermoelectric was studied. Combined with measurements on electrical resistivity and Seebeck coefficient, we show the use of a ZT map in selecting thermoelectrics. The commercial bulk material showed very good consistency and reliability compared to other bulk materials. Our goal is to develop a thermal transport properties database for the bulk thermoelectrics and make the information available to the research community and industry.
{"title":"Thermal conductivity measurements of bulk thermoelectric materials","authors":"H. Wang, W. Porter, J. Sharp","doi":"10.1109/ICT.2005.1519895","DOIUrl":"https://doi.org/10.1109/ICT.2005.1519895","url":null,"abstract":"Thermal conductivity is an important material property of the bulk thermoelectrics. To improve ZT a reduced thermal conductivity is always desired. However, there is no standard material for thermoelectrics and the test results, even on the same material, often show significant scatter. The scatter in thermal conductivity made reported ZT values uncertain and sometime unrepeatable. One of the reasons for the uncertainty is due to the microstructure differences resulting from sintering, heat treatment and other processing parameters. We selected commonly used bulk thermoelectric materials and conducted thermal conductivity measurements using the laser flash diffusivity and differential scanning calorimeter (DSC) systems. Thermal conductivity was measured as a function of temperature from room temperature to 500 K and back to room temperature. The effect of thermal cycling on the bulk thermoelectric was studied. Combined with measurements on electrical resistivity and Seebeck coefficient, we show the use of a ZT map in selecting thermoelectrics. The commercial bulk material showed very good consistency and reliability compared to other bulk materials. Our goal is to develop a thermal transport properties database for the bulk thermoelectrics and make the information available to the research community and industry.","PeriodicalId":422400,"journal":{"name":"ICT 2005. 24th International Conference on Thermoelectrics, 2005.","volume":"58 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2005-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114942980","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2005-06-19DOI: 10.1109/ICT.2005.1519975
T. Kamilov, D. K. Kabilov, I. S. Samiev, H. Husnutdinova, R.H. Kamilova, S. Dadamuhamedov, V. Klechkovskaya, A. Orekhov, M. Takeda
In the last years the great interest of scientists is focused on the study of higher manganese silicide films due to their high thermoelectric properties, good stability at high temperatures and combination with standard silicon planar technology. In this work formation and growth of the higher manganese suicide films were investigated. They were obtained by the deposition of flux of manganese atoms from the vapor phase on the silicon substrate surface and then by reactive diffusion between manganese atoms and silicon atoms from the substrate. These received results are compared with the data for the higher manganese suicide films grown by other methods. On the base of this analysis it is possible to suppose that the growth of the higher manganese silicide films by reactive diffusion method of manganese atoms from the vapor phase may be conditioned by mechanism of vapor-liquid-solid. This mechanism takes account of the fact that melting temperature of the small nucleus which size is about several nanometers is lower than the melting temperature of a bulk material. Besides, in contrast to other methods, the films of higher manganese silicide, which are formed by reactive diffusion method with the thickness up to micron, grow only in the interior of silicon substrate. This fact also can testify to the vapor-liquid-solid growth mechanism.
{"title":"About the mechanism of formation and growth of the higher manganese silicide films on silicon","authors":"T. Kamilov, D. K. Kabilov, I. S. Samiev, H. Husnutdinova, R.H. Kamilova, S. Dadamuhamedov, V. Klechkovskaya, A. Orekhov, M. Takeda","doi":"10.1109/ICT.2005.1519975","DOIUrl":"https://doi.org/10.1109/ICT.2005.1519975","url":null,"abstract":"In the last years the great interest of scientists is focused on the study of higher manganese silicide films due to their high thermoelectric properties, good stability at high temperatures and combination with standard silicon planar technology. In this work formation and growth of the higher manganese suicide films were investigated. They were obtained by the deposition of flux of manganese atoms from the vapor phase on the silicon substrate surface and then by reactive diffusion between manganese atoms and silicon atoms from the substrate. These received results are compared with the data for the higher manganese suicide films grown by other methods. On the base of this analysis it is possible to suppose that the growth of the higher manganese silicide films by reactive diffusion method of manganese atoms from the vapor phase may be conditioned by mechanism of vapor-liquid-solid. This mechanism takes account of the fact that melting temperature of the small nucleus which size is about several nanometers is lower than the melting temperature of a bulk material. Besides, in contrast to other methods, the films of higher manganese silicide, which are formed by reactive diffusion method with the thickness up to micron, grow only in the interior of silicon substrate. This fact also can testify to the vapor-liquid-solid growth mechanism.","PeriodicalId":422400,"journal":{"name":"ICT 2005. 24th International Conference on Thermoelectrics, 2005.","volume":"163 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2005-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129452288","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2005-06-19DOI: 10.1109/ICT.2005.1519959
E. Muller, S. Walczak, W. Seifert, C. Stiewe, G. Karpinski
Functionally graded and segmented thermoelements have been considered for long, aiming at improving the performance of thermogenerators (TEG) which are exposed to a large temperature difference. A numerical algorithm has been previously developed using the software MATHEMATICA and has been applied for modelling homogeneous and segmented Peltier elements. It is capable to calculate the exact temperature profile along a segmented element in a one-dimensional model. The algorithm is based on the constant properties assumption (CPA) in each of the segments and is also providing the opportunity of treating quasi-continuous gradients. Integral quantities like the voltage drop over the element and performance parameters like cooling power and C.O.P. (for a Peltier cooler) or output power and efficiency (for a TEG) are deduced taking into account the real temperature dependence of the materials properties. This algorithm was inserted in a loop (varying the current density) to determine optimum operation parameters at given temperature difference. Numerical parameter studies based on quasi-continuously grade elements, CPA in each of the segments, and preassuming constant volume average of the figure of merit over the whole element (ZT) provide guidelines for advantageous TE gradients in Peltier coolers and TEG. A practical example is illustrating the quantitative improvement of performance achievable by segmentation of a Peltier cooler.
{"title":"Numerical performance estimation of segmented thermoelectric elements","authors":"E. Muller, S. Walczak, W. Seifert, C. Stiewe, G. Karpinski","doi":"10.1109/ICT.2005.1519959","DOIUrl":"https://doi.org/10.1109/ICT.2005.1519959","url":null,"abstract":"Functionally graded and segmented thermoelements have been considered for long, aiming at improving the performance of thermogenerators (TEG) which are exposed to a large temperature difference. A numerical algorithm has been previously developed using the software MATHEMATICA and has been applied for modelling homogeneous and segmented Peltier elements. It is capable to calculate the exact temperature profile along a segmented element in a one-dimensional model. The algorithm is based on the constant properties assumption (CPA) in each of the segments and is also providing the opportunity of treating quasi-continuous gradients. Integral quantities like the voltage drop over the element and performance parameters like cooling power and C.O.P. (for a Peltier cooler) or output power and efficiency (for a TEG) are deduced taking into account the real temperature dependence of the materials properties. This algorithm was inserted in a loop (varying the current density) to determine optimum operation parameters at given temperature difference. Numerical parameter studies based on quasi-continuously grade elements, CPA in each of the segments, and preassuming constant volume average of the figure of merit over the whole element (ZT) provide guidelines for advantageous TE gradients in Peltier coolers and TEG. A practical example is illustrating the quantitative improvement of performance achievable by segmentation of a Peltier cooler.","PeriodicalId":422400,"journal":{"name":"ICT 2005. 24th International Conference on Thermoelectrics, 2005.","volume":"39 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2005-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130149825","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2005-06-19DOI: 10.1109/ICT.2005.1519880
N. Okinaka, T. Akiyama
The thermoelectric properties of a nonstoichiometric titanium oxide (TiO/sub 1.1/) are investigated in terms of materials for high-temperature thermoelectric conversion. The electrical conductivity, /spl sigma/, of TiO/sub 1.1/ increases up to ca. 9000 S/m at 800 /spl deg/C, is showing semiconducting behavior. The Seebeck coefficient, /spl alpha/, of TiO/sub 1.1/ shows a general trend in which the absolute value increases gradually from ca. 0.4 mV/K at 300/spl deg/C to ca. 1.0 mV/K at 950/spl deg/C. As a consequence, the power factor, /spl alpha//sup 2//spl sigma/, reaches ca. 8.6/spl times/10/sup -3/ W/(K/sup 2//spl middot/m), the largest value of all reported oxide materials. The thermal conductivity, /spl kappa/, of TiO/sub 1.1/ increases with temperature, from ca. 1.3 W/(K/spl middot/m) at 300/spl deg/C to ca. 7.1 W/(K/spl middot/m) at 950/spl deg/C. In spite of the considerably large values of /spl kappa/, the figure of merit, Z=/spl alpha//sup 2//spl sigma///spl kappa/, reaches 1.6/spl times/10/sup -3/ K/sup -1/ for TiO/sub 1.1/ at 700/spl deg/ C. The extremely large power factor of TiO/sub 1.1/ compared to other metal oxides can be attributed to the large carrier density. The dimensionless figure of merit, ZT, of 1.64 attained by TiO/sub 1.1/ at 800/spl deg/C is the largest value of all reported other thermoelectric materials in this temperature region. And that TiO/sub 1.1/ has ZT values of nearly unity or greater in the range of 500/spl deg/C to 1000/spl deg/C, demonstrates the usefulness of the nonstoichiometric titanium oxides for high-temperature thermoelectric conversion.
{"title":"Thermoelectric properties of nonstoichiometric TiO as a promising oxide material for high-temperature thermoelectric conversion","authors":"N. Okinaka, T. Akiyama","doi":"10.1109/ICT.2005.1519880","DOIUrl":"https://doi.org/10.1109/ICT.2005.1519880","url":null,"abstract":"The thermoelectric properties of a nonstoichiometric titanium oxide (TiO/sub 1.1/) are investigated in terms of materials for high-temperature thermoelectric conversion. The electrical conductivity, /spl sigma/, of TiO/sub 1.1/ increases up to ca. 9000 S/m at 800 /spl deg/C, is showing semiconducting behavior. The Seebeck coefficient, /spl alpha/, of TiO/sub 1.1/ shows a general trend in which the absolute value increases gradually from ca. 0.4 mV/K at 300/spl deg/C to ca. 1.0 mV/K at 950/spl deg/C. As a consequence, the power factor, /spl alpha//sup 2//spl sigma/, reaches ca. 8.6/spl times/10/sup -3/ W/(K/sup 2//spl middot/m), the largest value of all reported oxide materials. The thermal conductivity, /spl kappa/, of TiO/sub 1.1/ increases with temperature, from ca. 1.3 W/(K/spl middot/m) at 300/spl deg/C to ca. 7.1 W/(K/spl middot/m) at 950/spl deg/C. In spite of the considerably large values of /spl kappa/, the figure of merit, Z=/spl alpha//sup 2//spl sigma///spl kappa/, reaches 1.6/spl times/10/sup -3/ K/sup -1/ for TiO/sub 1.1/ at 700/spl deg/ C. The extremely large power factor of TiO/sub 1.1/ compared to other metal oxides can be attributed to the large carrier density. The dimensionless figure of merit, ZT, of 1.64 attained by TiO/sub 1.1/ at 800/spl deg/C is the largest value of all reported other thermoelectric materials in this temperature region. And that TiO/sub 1.1/ has ZT values of nearly unity or greater in the range of 500/spl deg/C to 1000/spl deg/C, demonstrates the usefulness of the nonstoichiometric titanium oxides for high-temperature thermoelectric conversion.","PeriodicalId":422400,"journal":{"name":"ICT 2005. 24th International Conference on Thermoelectrics, 2005.","volume":"22 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2005-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130338430","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2005-06-19DOI: 10.1109/ICT.2005.1519985
P. Hagelstein, Y. Kucherov
We have developed a nonlocal generalization of the Onsager current relation to study the enhancement of the open-circuit voltage observed in InSb thermal diode experiments. Numerical solutions are obtained by brute force. Nonlocal effects produce an apparent enhancement of the thermopower in regions where the doping concentration changes. Models show voltage drops associated with npn barriers similar to experiment below 350 K, but are not as great as experimental results at high temperature near 600 K. This is thought to be due to thermal drops at the barrier not accounted for so far.
{"title":"Models for the thermal diode open-circuit voltage","authors":"P. Hagelstein, Y. Kucherov","doi":"10.1109/ICT.2005.1519985","DOIUrl":"https://doi.org/10.1109/ICT.2005.1519985","url":null,"abstract":"We have developed a nonlocal generalization of the Onsager current relation to study the enhancement of the open-circuit voltage observed in InSb thermal diode experiments. Numerical solutions are obtained by brute force. Nonlocal effects produce an apparent enhancement of the thermopower in regions where the doping concentration changes. Models show voltage drops associated with npn barriers similar to experiment below 350 K, but are not as great as experimental results at high temperature near 600 K. This is thought to be due to thermal drops at the barrier not accounted for so far.","PeriodicalId":422400,"journal":{"name":"ICT 2005. 24th International Conference on Thermoelectrics, 2005.","volume":"40 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2005-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130071935","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2005-06-19DOI: 10.1109/ICT.2005.1519879
J.E. Rodriguez
A study of thermoelectric power factor, PF=S/sup 2///spl rho/, of polycrystalline YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) samples synthesized from oxides by solid state reaction have been carried out. The Seebeck coefficient, S(T) and electrical resistivity, /spl rho/(T) were measured in the temperature range between 77 K and 300 K. The oxygen present in the samples was modified by means of an annealing process at 600/spl deg/C for different periods of time. The Seebeck coefficient is positive in whole measured temperature range and shows a linear behavior with the temperature, its magnitude increases from 30 /spl mu/V/K for the samples annealed during one hour to 1000 /spl mu/V/K for the samples annealed through 50 hours. The behavior of electrical resistivity changes from metallic to semiconducting as the annealing time is increasing. The magnitude of /spl rho/(T) increases from 10/sup -3/ /spl Omega/-cm to 10/sup -1/ /spl Omega/-cm as the annealing time increases. The thermoelectric power factor reaches values around 18 /spl mu/W/K/sup 2/cm cm in the samples annealed for 30 hours. The behavior of the transport properties suggests that the carrier density and the scattering mechanisms can be modified by decreasing the oxygen level, which open the possibility of use these kind of materials as active thermoelements.
{"title":"Thermoelectric power factor of YBCO polycrystalline samples","authors":"J.E. Rodriguez","doi":"10.1109/ICT.2005.1519879","DOIUrl":"https://doi.org/10.1109/ICT.2005.1519879","url":null,"abstract":"A study of thermoelectric power factor, PF=S/sup 2///spl rho/, of polycrystalline YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) samples synthesized from oxides by solid state reaction have been carried out. The Seebeck coefficient, S(T) and electrical resistivity, /spl rho/(T) were measured in the temperature range between 77 K and 300 K. The oxygen present in the samples was modified by means of an annealing process at 600/spl deg/C for different periods of time. The Seebeck coefficient is positive in whole measured temperature range and shows a linear behavior with the temperature, its magnitude increases from 30 /spl mu/V/K for the samples annealed during one hour to 1000 /spl mu/V/K for the samples annealed through 50 hours. The behavior of electrical resistivity changes from metallic to semiconducting as the annealing time is increasing. The magnitude of /spl rho/(T) increases from 10/sup -3/ /spl Omega/-cm to 10/sup -1/ /spl Omega/-cm as the annealing time increases. The thermoelectric power factor reaches values around 18 /spl mu/W/K/sup 2/cm cm in the samples annealed for 30 hours. The behavior of the transport properties suggests that the carrier density and the scattering mechanisms can be modified by decreasing the oxygen level, which open the possibility of use these kind of materials as active thermoelements.","PeriodicalId":422400,"journal":{"name":"ICT 2005. 24th International Conference on Thermoelectrics, 2005.","volume":"33 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2005-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125382838","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2005-06-19DOI: 10.1109/ICT.2005.1519964
T. Mori, T. Tanaka
Investigation is being done on the high temperature thermoelectric properties of some new rare earth B12 icosahedra cluster-containing compounds. Doping effects on the TE properties in such systems were investigated for the first time. A series of heavily Nb-doped YB66 single crystals were grown by the floating zone method. The doping dependence on the thermoelectric properties was not monotonic and appears to be complex. As a result of doping, the room temperature resistivity showed a sizable reduction together with a sizable reduction of T0 (increase in D(EF) or elongation of ξ). At room temperature the Nb-doped YB66 sample with 89% site occupancy yielded a factor 3 increase over the power factor of non-doped YB66. However, in the important high temperature region (for these compounds) the non-doped sample actually exhibited the highest power factor for T>550 K. This result is interesting as it advocates manufacturing a high T0, despite meaning an actual higher initial resistivity, for these compounds when considering extremely high temperature properties (which is obvious considering the meaning of T0). Furthermore, due to a special structural feature of YB66, the thermal conductivity actually increases with doping of transition metals and therefore, from these results YB66 is judged to not be a feasible system to pursue among these rare earth boron cluster compounds.
{"title":"High temperature thermoelectric properties of heavily Nb-doped Yb/sub 66/ single crystals","authors":"T. Mori, T. Tanaka","doi":"10.1109/ICT.2005.1519964","DOIUrl":"https://doi.org/10.1109/ICT.2005.1519964","url":null,"abstract":"Investigation is being done on the high temperature thermoelectric properties of some new rare earth B12 icosahedra cluster-containing compounds. Doping effects on the TE properties in such systems were investigated for the first time. A series of heavily Nb-doped YB66 single crystals were grown by the floating zone method. The doping dependence on the thermoelectric properties was not monotonic and appears to be complex. As a result of doping, the room temperature resistivity showed a sizable reduction together with a sizable reduction of T0 (increase in D(EF) or elongation of ξ). At room temperature the Nb-doped YB66 sample with 89% site occupancy yielded a factor 3 increase over the power factor of non-doped YB66. However, in the important high temperature region (for these compounds) the non-doped sample actually exhibited the highest power factor for T>550 K. This result is interesting as it advocates manufacturing a high T0, despite meaning an actual higher initial resistivity, for these compounds when considering extremely high temperature properties (which is obvious considering the meaning of T0). Furthermore, due to a special structural feature of YB66, the thermal conductivity actually increases with doping of transition metals and therefore, from these results YB66 is judged to not be a feasible system to pursue among these rare earth boron cluster compounds.","PeriodicalId":422400,"journal":{"name":"ICT 2005. 24th International Conference on Thermoelectrics, 2005.","volume":"351 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2005-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123541436","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2005-06-19DOI: 10.1109/ICT.2005.1519969
P. Konstantinov, L. Prokofieva, M. Fedorov, D. Severin, Y. Ravich, V. Kompaniets, V. Chistyakov
The Hall factor and thermoelectric properties of n-Bi/sub 2/Te/sub 2.7/Se/sub 0.3/ solid solution with the room-temperature Seebeck coefficient S = 212 /spl mu/V/K have been studied in the temperature range 77-350 K. The observed temperature dependences demonstrate some specific features, which were found earlier in samples with lower electron density N. The effect of these specific features on the thermoelectric figure of merit Z appears to be more favorable for the sample under study: this sample is most efficient in the temperature range 120-340 K, the average value of ZT is 0.71. It is found that the rise of density N enhances the factor responsible for the effective mass decreasing as temperature increases; this effect appears when the analysis is made in terms of a single-band parabolic model with N = const(T). We believe that the most probable reason for the unusual behavior of properties is a complex structure of the electron spectrum. Calculations have been made, and the obtained temperature dependences of transport coefficients show a good agreement with the experimental data for two samples of the mentioned composition with different electron densities. The calculations were performed in terms of a two-band model and acoustic scattering, with the account for anisotropy and nonparabolicity of the light-electron spectrum.
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